U.S. Pat. No. 4,346,227 to Terahara et al. disclosed a pravastatin which can be obtained by fermentation of compactin using a variety of microorganisms. After fermentation, pravastatin was separated from the fermentation broth by acidifying the broth to a pH of 3 and extracting pravastatin and other non-hydrophilic organics with ethyl acetate, followed by washing with brine. The pravastatin free acid was lactonized by addition of a catalytic amount of trifluoroacetic acid, then neutralized with dilute sodium bicarbonate, dried over sodium sulfate and evaporated to dryness. The residue was purified by preparative reverse-phase high performance liquid chromatography. However, such a reverse-phase HPLC is not an economical method of purification for large-scale preparation of a chemical compound as evaluated by those skilled in the art.
Meanwhile, the pravastatin is unstable in the acidic aqueous solution and will be easily decomposed into 3-Hydroxy-iso-compactin or pravastatin lactone or other impurities. During the extraction for the purification of pravastatin sodium, emulsion phenomena will also occur to deteriorate the product purity and quality. Therefore, the process of the prior art is not suitable for commercial mass production.
The present inventor has found the drawbacks of the prior art and invented the present process for stably purifying pravastatin sodium from a fermentation broth.
The object of the present invention is to provide a process for stably purifying pravastatin sodium comprising the steps of:
a. clarifying a fermentation broth containing pravastatin sodium by centrifugation or filtration to obtain a supernatant or filtrate containing the pravastatin sodium; and adjusting the supernatant or filtrate to be basic having pH value ranging from pH 10xcx9c13;
b. adsorbing the pravastatin sodium with non-ionic resin which is then washed with water; eluting the pravastatin sodium as adsorbed on the resin by water-soluble organic solvent to obtain pravastatin sodium fraction; and concentrating the fraction to be pravastatin sodium concentrate;
c. treating the concentrate with water-soluble anti-solvent or inorganic salt to form a precipitate of pravastatin sodium; and
d. recrystallizing the precipitate for making pravastatin sodium crystal with high purity and high yield.